There were a few soft recommendations. Specifically I remember an ER doctor in 2019 saying vitamin D seemed to be a differentiator in the sample of cases he was seeing in the ER (everyone was starting to panic) and the CDC walking it back as unsubstantiated. I mentioned it at work, then 10 days later my boss's boss asked me where I had heard it, because he had heard the same thing.
There have been a number of people on HN who have attributed any measurable COVID benefit of Vitamin D, to a confounding variable, as recently as 3 months ago - https://news.ycombinator.com/item?id=44705486 The Big Vitamin D Mistake
One of the best treatments is interferon. It's something you will also produce yourself, with therapeutic effect, if exposited to sunlight or the infrared light used in red light therapy. Here's a video about it, from a continuing education provider: https://www.youtube.com/watch?v=oRkxH56LqCo
